This work is a continuation of a program of research designed to identify, characterize and localize specific peptidases involved in the maturation and degradation of peptide neurotransmitters in mammalian brain. We will use dipeptidyl aminopeptidase II(DAP II) as a model system for the biochemical characterization and histochemical localization of specific neuropeptidases. By means of biochemical fractionation techniques, we will purity DAP II. Pure preparations will be characterized with respect to activity towards various neuropeptides and synthetic substrates. Synthesis of specific inhibitors will be developed as a means of determining the physiologic role of the enzyme. We will also fractionate brain extracts and using kinetic and biochemical parameters identify and characterize the endogenous substrate of DAP II. Ultrastructural studies at the electron microscope level will be initiated in order to determine the intracellular distribution of DAP II. The mechanisms by which colchicine produces a paradoxical redistribution of neuronal DAP II will be studied by means of histochemistry and electron microscopy. We will determine whether DAP II plays a role in the etiology of amyotrophic lateral sclerosis (ALS) and with specific inhibitors of DAP II determine whether an animal model for this disease can be obtained. The scientific disciplines involved in these studies are: histochemistry, immunohystochemistry, biochemistry, neurobiology, neurochemistry, cell biology, and neuroanatomy.